Avionics products in an aircraft are uniquely motivated to minimize (1) weight (to support safe weight attributes and to maximize payload); (2) size (uniquely limited available space); (3) electrical power usage (limited electrical power available in an aircraft, particularly under emergency power conditions); (4) failure rates (to assure safety); and (5) complexity of operation (given the complexity otherwise inherent in flight operations). Products that integrate functionality contribute to achieving these objectives.
Aircraft have historically been equipped with typically a collection of mechanical or electro-mechanical flight instrument gauges that give a pilot information about the aircraft's position, orientation, speeds, and performance. The gauges commonly provide quite limited breadth of functionality—typically only a single function. For example, the instrument panel of an aircraft employing such gauges might include an attitude indicator that shows the aircraft's orientation relative to the horizon, an altimeter that gives information about the aircraft's height above some reference level (e.g. sea-level) by measuring the local air pressure, an airspeed indicator that shows the aircraft's speed relative to the surrounding air, a heading indicator or magnetic compass that displays the direction the aircraft is pointing relative to north, or a turn and bank indicator that displays the direction of turn and rate of turn of the aircraft.
More recently, integrated avionics systems have been replacing the [electro-]mechanical instrument gauges summarized above with one or more electronic displays for displaying primary flight information such as attitude, altitude, heading, vertical speed, and so forth, to the pilot. Integrated avionics systems may include one or more primary flight displays (PFD) and one or more multifunction displays (MFD). A representative PFD displays primary flight and selected navigation information that is typically received from one or more sensor systems such as an attitude heading reference systems (AHRS), an inertial navigation system (INS), one or more air data computers (ADC) and/or navigation sensors. A representative MFD displays information for navigation and for broad situational awareness such as navigation routes, flight plans, information about aids to navigation (including airports), moving maps, weather information, terrain and obstacle information, traffic information, engine and other aircraft systems information, and so forth. In some instantiations, a display that is normally used as a PFD or MFD may operate, for example under failure reversion circumstances, in a mode of operation during which PFD and MFD information are shown together on a display in some composite manner.